PIJIJIAPAN: Mexican President Enrique Peña Nieto, has declared three days of national mourning after the strongest earthquake measuring 8.2 on the Richter scale struck off the country in a century that left at least 61 people dead. The powerful quake has affected at least 50 million people in 12 states.

President Nieto, in a televised address stated that 61 people were killed - 45 in Oaxaca state, 12 in Chiapas and four in Tabasco.

"The temblor felt by about 50 million people across the country was the strongest earthquake Mexico has experienced in 100 years. Widespread destruction has been caused by the earthquake and about 1.85 million affected people are living under harsh conditions with no electricity and shortage of water," President Nieto said.

The earthquake of magnitude 8.1 quake, which was felt as far as Mexico City and Guatemala City, was also registered off Mexico's southern coast just as heavy rains from Hurricane Katia lashed the east. The epicentre was in the Pacific Ocean, some 600 miles (1,000 KMs) southeast of the capital and 74 miles (120 KMs) off the coast, CNN reported.

More than 600 aftershocks have been recorded since the earthquake struck off the Mexico's southern Pacific coast just before midnight on Thursday local time. Mexican officials have now upgraded the quake to 8.2 in magnitude.

Mexico's President said, "The Country's army, marines and federal police have been mobilised and rescue and relief operations are in full swing and the government has also released lists of approved food and goods that people should bring to Red Cross' emergency centres to help with relief efforts.

The President said, "Authorities are working to resume the supply of water and food and provide medical attention to those in need. The government would help people rebuild and called on people to come together."

The worst-hit city is Juchitan, in the southern state of Oaxaca, where at least 36 bodies were pulled from ruins, and a large number of buildings collapsed, including the city's town hall. Oaxaca is one of the three states near the quake epicentre off the coast.

The earthquake triggered tsunami waves as high as 3.3 feet at the port of Salina Cruz in Oaxaca, according to the US National Weather Service's Pacific Tsunami Warning.

As many as 8,000 people have been evacuated by the Mexican navy so far.